The present invention relates generally to a gas turbine, and more particularly relates to a gas turbine for an air storage facility having at least one turbine stage through which axially flows a, preferably hot,, power gas and with at least one balance piston to equalize an axial thrust. The balance piston is arranged at the shaft of the turbine adjacent to a plurality of pressurized-fluid chambers.
To equalize the axial thrust, gas turbines often have shaft balance pistons which will compensate, or at least substantially compensate, for the axial thrust occurring during operations by correspondingly pressure loading the piston areas. In this way, the existing axial bearings are unburdened. It is also known to cool the parts of gas turbines which are under high thermal stresses such as for example, the supports of the entrance blades and/or the guide vanes.
It is an object of the present invention to provide a gas turbine having an efficient thrust-balancing and cooling system which needs a minimum of structural components and has a low power-loss factor. Such a gas turbine should also be very reliable in operation and should satisfy all requirements arising in the course of gas turbine operations.
The present invention solves this problem by having a first pressurized fluid chamber being arranged adjacent to the power-gas intake of the turbine stage and separated from at least one additional pressurized fluid chamber by means of a first transfer gasket which interacts with the balance piston. The first fluid pressure chamber can be provided with a gaseous pressure fluid, preferably with air, having a pressure that is higher than the pressure of the power gas within the region of the power-gas intake. At least one cooling system of the gas turbine is connected to the additional pressurized fluid chamber for the delivery of a coolant. A slot of the first transfer gasket is selected in such manner that the pressure difference between the fluid pressure chambers can be set to bring about an at least partial equalization of the axial thrust by way of the balance piston.
The individual fluid pressure chambers, which are adjacent to the balance piston, are loaded in succession by the pressurized fluid being delivered, with the pressurized fluid flowing by way of the slot of the transfer gasket from one fluid pressure chamber to another fluid pressure chamber.
Since the coolant for the cooling system is taken from the fluid pressure chamber which is arranged successively to the balance piston, a pressure gradient will arise between the fluid pressure chambers. This pressure gradient will cause, in co-action with the balance piston, the equalization of the axial thrust. Since the pressurized fluid after flowing through the fluid pressure chambers, is conveyed to the cooling system or systems having a coolant deficiency, a simple coolant supply is being insured. Furthermore, the pressurized fluid is being additionally utilized as a coolant. The use of the slot of the transfer gasket for the adjustment of the fluid pressure flow and accordingly of the pressure gradient eliminates the need for any additional throttling elements so that the gas turbine of the present invention has a simplified overall layout.
The transfer gaskets of the present invention include but are not liminted to contact-free seals or sealing arrangements such as split seals, labyrinth seals or combined slot-labyrinth seals.
If the gas turbine has several turbine stages and balance pistons, it will be advantageous to provide several additional fluid pressure chambers arranged in series. Each chamber is adjacent to an additional balance piston and is separated from each other by an additional transfer gasket which co-acts with an additional balance piston. In this way, the cooling system is connected to one of the additional fluid pressure chambers and the slots of the transfer gaskets are selected so that a pressure difference can be set in such a manner between the pressure-medium chambers that it will, at least partially, equalize the axial thrust.
All fluid pressure chambers are connected in series and are subjected to a flow-through by the pressurized fluid so that pressure is exerted upon each of the balance pistons. These individual pressures will collectively bring about the thrust equalization. In this way, the cooling system is connected to one of the pressurized fluid chambers. It will be advantageous if the cooling system is also provided for a turbine stage that follows the first turbine stage. It will further be advantageous to assign one cooling system to one of the successively arranged turbine stages and to connect it in each situation to one of the additional fluid pressure chambers.
An especially preferred further development of the invention consists of an arrangement wherein the cooling system of the second turbine stage is connected to the second fluid pressure chamber and wherein the cooling system of the third turbine stage is connnected to the third fluid pressure chamber and so on as viewed and counted from the power-gas intake.
If the cooling system is connected to a fluid pressure chamber which is formed with the aid of two balance pistons, it will be advantageous, for the purpose of insuring a fluid pressure flow up to and into the final fluid pressure chamber, to connect the last fluid pressure chamber with a waste gas duct. Since the gas pressure within this duct represents the lowest gas pressure of the turbine system, a pressure gradient from the first up to the last fluid pressure chamber will be insured.
Another expedient further development of the present invention is an arrangement wherein the first fluid pressure chamber forms in conjunction with the area enclosing the first turbine stage a single unit of volume, thus simplifying the layout as well as the cooling of the first turbine stage.
If air is used as the pressurized fluid, the hot power gases produced in the combustion chambers can be utilized in a very simple manner by connecting the first fluid pressure chamber with the compressed-air supply for the combustion chamber of the first turbine stage. In this way, a fluid pressure flow is obtained. It will be very expedient in this case to install a heat exchanger between the first pressure-medium chamber and the compressed-air supply. The heat exchanger is preferably placed within the exhaust flow of the gas turbine. In this manner the air provided as pressurized fluid is being pre-heated so that sudden changes in temperature within the turbine are avoided and a uniform heating of the loaded turbine parts is promoted.
In order to protect the cooling system from excess pressures which could occur in case of excessive venting by the transfer gaskets of the balance pistons, it will be advantageous to equip the cooling system with at least one adjustable safety valve which will connect the cooling system with a bridging area if the pressure difference goes beyond a pre-set value. The blowoff from the safety valve will enter a bridging area which connects two turbine stages at their gas sides so that the opening of the safety valve will only lead to very minor power losses.
In order to insure a sufficient supply of coolant, it will be advantageous to provide the cooling system with at least one adjustable by-pass valve which is located within a pipe line connecting the cooling system and the pressurized fluid duct and which will open if the pressure difference between the cooling system and the bridging area drops below a pre-set value. This measure will prevent any deficiency of coolant within the cooling system.
The gas turbine may comprise at least one air-cooled combustion chamber for the first turbine stage arranged at the turbine housing. In such an arrangement, an especially preferred further development of the invention is then characterized by the features that the single unit of volume is traversed by a transition piece leading to the heating gas intake of the first turbine stage, entering in telescopic fashion and forming an air gap in the open end of the first combustion chamber. Furthermore, the single unit of volume is sealed off by at least two throttles from the air space which surrounds the combustion chamber and can be charged by the air of combustion. The throttles are placed in series within the air space and define a special area, with the air gap leading into this area.
Such an arrangement makes possible a cooling of the transition piece carrying the hot power gases. Having the transition of the combustion chamber end connected to the transition piece in telescopic fashion will allow the expansion of these parts independently of each other. Since the air space surrounding the combustion chamber is sealed off only by two throttles which are arranged one after another at a distance within the air space, the air or coolant supply reaching the special area will be sufficient for the cooling of the sealing sites. Furthermore, since the transition piece ends within the special area, air or coolant respectively will be drawn in through the air gap from the special area into the transition piece due to an injector effect of the combustion-chamber flow. The quantity of air or coolant joining the power gas flow is not controlled at all by the size of the air gap but is solely determined by the venting capability of the throttles. The size of the air gap can therefore be chosen exclusively on the basis of structural aspects.
A particularly simple construction will be feasible if the first throttle, which is located adjacent to the single unit of volume, has the shape of a flat annular body that embraces and is fastened to the transition piece. Furthermore, the first throttle engages a ring-gap of an outer ring with a first throttle-gap between the outer ring and the outer wall of the air space being left unobstructed. The outer ring consists of at least two ring segments which are joined to each other by a connecting ring. This structural design makes it possible to keep the free space of the air gap to a minimum despite the wide differences in heat expansion between the turbine housing and the transition piece. An adjustment of the size of the throttle gap is made possible at the time of assembly in accordance with the specific requirements by the proper selection of the ring segments.
The other throttle can be formed by a plain ring-gap between the combustion chamber wall and a flat ring supported by the outer wall of the air space because these components are subjected to substantially identical temperatures at like times. Accordingly, wide differences in heat expansion therefore do not arise. It will be advantageous, however, if the second throttle is provided with a second throttle-gap. The second throttle-gap is formed between the combustion chamber wall and a cylindrical hollow body which surrounds the combustion chamber wall and is supported by an annular partition traversing the air space and fastened to the outer wall of the air space. It will be expedient to arrange the hollow body between the combustion chamber wall and the widened upper end of the transition piece.
Another preferred further development of the invention is represented by an arrangement where, following the cut-off of the power gas supply, the turbine stages and the last guide vane set of the last turbine stage can be supplied individually or in combination with a gaseous cooling fluid to dissipate the windage heat which is building up during the deceleration of the turbine.
If the gas turbine is equipped with an air storage unit, it will be advantageous to utilize compressed air, withdrawn from the air storage unit, as the cooling fluid.